In 3rd Generation Partnership Project (3GPP) Long term Evolution (LTE) wireless communication systems, a user equipment (UE) transmits power headroom (PH) reports to the base station (also known as eNB in 3GPP LTE) to indicate the power headroom (PH) available for UE transmissions. The UE computes its PH according to the following formula:PHc(i)=PCMAX,c,(i)−{10 log10(MPUSCH,c(i))+PO_PUSCH,c(j)+αc(j)·PL+ΔTF,c(i)+fc(i)}
where “i” is the subframe and “c” is a component carrier (CC) or serving cell for which the PH is reported. MPUSCH is a Physical Uplink Shared Channel (PUSCH) resource allocation bandwidth signaled to the UE in terms of a number of resource blocks allocated to the UE in the sub-frame, PL is a downlink (DL) path loss estimate, P0_PUSCH and α are open loop power control parameters, f(i) is a power control state obtained by accumulating closed loop power control commands and ΔTF is the Modulation and Coding Scheme (MCS) based transmission power offset. A resource block has dimensions of subcarriers by symbols, where 12 subcarriers in the frequency domain and 6 or 7 symbols in the time domain form each resource block. PCMAM is the configured maximum output power for the UE and is a function of several parameters defined in 3GPP 36.101 including P_PowerClass (the nominal UE maximum transmit power), PEMAX (a transmit power limit signaled by the eNB to the UE) , MPR (Maximum Power Reduction), A-MPR (Additional-Maximum Power Reduction), and ΔTC (a maximum power adjustment made by the UE based on the frequency location of its carrier ). In LTE Release 10 (Rel-10), a separate value of PCMAX (PCMAX, c) for each aggregated uplink (UL) component carrier is assumed. In LTE Rel-10, in addition to PH, PCMAX is also reported by the UE to the eNB. LTE Release 8 (Rel-8), PCMAX is defined by the equation below:MIN{(PEMAX−ΔTC),(PPowerClass−MPR−A-MPR−ΔTC)}≦PCMAX≦MIN{PEMAX,PPowerClass}
Here, MPR is a maximum power reduction (i.e., the UE may back-off its transmission power between 0 dB and MPR dB) allowed for the UE to account for transmissions with higher order modulation and larger carrier bandwidth. A-MPR is an additional maximum power reduction allowed for the UE when additional Adjacent Channel Leakage Ratio (ACLR) and spectrum emission requirements are signaled by the base station. The equation for PCMAX illustrates that the UE is allowed to apply a power back-off between 0 dB and (MPR+A-MPR+ΔTC) dB to determine its PCMAX value. The value of the back-off applied can vary between different UEs based on their RF implementation, so, the exact value of the power back-off applied by a particular UE to account for MPR and A-MPR allowances is not known to the eNB. The eNB can, at best, assume that the back-off applied by the UE is smaller than MPR+A-MPR+ΔTC depending on the MCS level, Resource Block (RB) allocation within a given frequency band and additionally signaled ACLR and spectrum emission requirements.
LTE Rel-10 UL transmission mechanisms such as simultaneous transmission of the Physical Uplink Control Chanel (PUCCH) and PUSCH or transmission of multiple non-contiguous clusters of contiguous PUSCH Resource blocks (typically referred to as clustered PUSCH or non-contiguous PUSCH) would generate additional inter-modulation (IM) products in the UE transmitter chain. Under these circumstances, a new transmitter power back-off (in addition to the back-offs already required for LTE Rel-8) would likely be required to address the IM issues in LTE Rel-10. The value of the new back-off can be 4 dB to 10 dB depending on the number of resource blocks allocated to the UE and the location thereof. This new back-off is also expected to be included by the UE while computing PCMAX,c in LTE Rel-10.
The UE may also need to apply yet another new additional power back-off based on its RB allocation when configured for dual radio access technology (RAT) transmissions (e.g., simultaneous LTE and 1xRTT transmissions). There may be other scenarios where the UE may need to apply additional power back-off for certain RB allocations. Such scenarios include simultaneous LTE and WiFi transmissions and simultaneous LTE and Bluetooth transmissions.
Including these new additional back-off values in PCMAX computations and reporting the PCMAX (and also optionally the PH that is computed based on the PCMAX) to the eNB will help the eNB to better understand UEs transmission power and transmission power headroom available. The eNB can use this information for more accurate scheduling and power control that increases network capacity.
In general, UEs in future LTE systems need to apply different power back-offs for different RB allocations to either meet ACLR and spectral emission requirements or to manage various terminal power management requirements or both. ACLR and spectral emission requirements must generally be met for simultaneous PUSCH and PUCCH transmissions or for non-contiguous PUSCH transmissions. Terminal power management requirements may be related to simultaneous LTE and 1xRTT transmissions, simultaneous LTE and WiFi transmissions, or simultaneous LTE and Bluetooth transmissions.
LTE-A supports sending multiple separate PH reports in a given sub-frame with each report corresponding to a particular serving cell associated with a particular component carrier as described in 3GPP contributions R2-105960, R1-094274, R1-105761 and R1-105802. The prior art identified does not discuss sending multiple PH and PCMAX reports in a given sub-frame for various subsets of PUSCH RBs (i.e., resource block groups) within a single carrier.
The various aspects, features and advantages of the invention will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.